When aerosol cans dispense their contents a static charge can be generated. Because flammable propellants are often used, there may be the potential for igniting the output cloud through a static electric discharge. Because of this buildup of electrostatic charge, it has become necessary to measure the electrostatic charge in aerosol systems, see, for example J. R. Greaves and B. Makin, "A grid collection method for the measurement of electrostatic charge in aerosol systems", Aerosol Age February 1980.